Today many different types of plate heat exchangers exist and are employed in various applications depending on their type. Some types of plate heat exchangers have a casing that forms a sealed enclosure in which heat transfer plates that are joined are arranged. The heat transfer plates form a stack of heat transfer plates where alternating first and second flow paths for a first and a second fluid are formed in between the heat transfer plates.
Since the heat transfer plates are surrounded by a casing, the heat exchanger may withstand high pressure levels in comparison with many other types of plate heat exchangers. Some examples of heat exchangers with a casing that surrounds heat transfer plates are found in patent documents EP2508831 and EP2527775. The plate heat exchangers disclosed by these documents handle high pressure levels well. However, in some applications the casing has to be relatively thick to be able to handle the desired pressure levels, which increases the total weight as well as the overall cost of the heat exchanger. Also, the heat transfer plates within the casing must be designed for withstanding high pressure levels. However, at the same time the heat transfer plates must be able to efficiency transfer heat. Generally, the heat transfer plates are of a so called chevron type, i.e. have a pattern with a set of elongated ridges and grooves that are inclined to another set of elongated ridges and grooves (sometimes referred to as herringbone pattern).
New types of plate heat exchangers as well as heat transfer plates that may withstand high pressure levels are needed. The heat exchangers and heat transfer plates should preferably require relatively little material for their structure while still ensuring the heat is efficiently transferred between the heat transfer plates.